The Michael Corleone story: Michael (Al Pacino) realizes that his brother Fredo (John Cazale) was involved in an attempt to kill him, and orders Fredo to be shot from behind while fishing. Michael also ostracizes Kay (Diane Keaton), after finding out that she had an abortion without telling him. The movie ends with Michael sitting by himself by Lake Tahoe, with obvious 'ghosts' haunting his conscience.

The Vito Corleone story: A younger Vito Corleone (Robert DeNiro) kills the
local Don, which raises his position in life, as well as influence. Years
later, returning to Italy with his family as a sucessful mobster as well as
importer of olive oil; he takes his revenge on the Don who killed his family by
stabbing him in the chest.
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